Coupling between waveguides using arcuate slots with vacuum-tight dielectric window in region of low electric field



Oct. 19, 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHTDIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD 3 Sheets-Sheet 1 FiledJan. 15, 1964 Fig.1

Oct. 19, 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHTDIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD Filed Jan. 15, 1964 5Sheets-Sheet 2 Fig.5 2

O 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHTDIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD Filed Jan. 15, 1964 3Sheets-Sheet 5 Patented 3,213,394 COUPLING BETWEEN WAVEGUIDES USING AR-CUATE SLOTS WITH VACUUM-TIGHT DIELEC- TRIC WINDOW IN REGION OF LOWELECTRIC FIELD Roland Liebscher, Poing, near Munich, and ErichMayerhofer and Werner Veith, Munich, Germany, assignors to Siemens &Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation ofGermany Filed Jan. 15, 1964, Ser. No. 337,806 Claims priority,application Germany, Jan. 18, 1963, S 83,307 26 Claims. (Cl. 333-98) Theinvention disclosed herein is concerned with a transmission system forultra high frequency electromagnetic waves, especially for use inconnection with high capacity ultra high frequency tubes, comprising twowave guides which are mutually connected by way of at least oneslot-shaped coupling opening which is' closed vacuum-tight by means of adielectric window through which the electromagnetic wave energy passesfrom one wave guide to the other.

It is in connection with high capacity travelling Wave tubes customaryto use for the coupling and decoupling of high frequency energy,:cross-sectionally preferably rectangular Wave guides. The wave guidesare directly connected with the delay line in order to avoid contactingditficulties. A part of the wave guides forms in this man ner, a part ofthe vacuum envelope of the tube and therefore must be closedvacuum-tight by means of windows made of dielectric material whichwindows are permeable by the high frequency waves. It is therebyimportant that the unavoidable losses occurring in the dielectric windowremain small over as great a frequency range as possible. This may beachieved provided that no particular electric field increases appear atthe window due to resonance elfects occurring at the desiredtransmission range.

In previously known transmission systems for electromagnetic ultra highfrequency waves, comprising two Wave guides and a dielectric window forclosing one wave guide with respect to the other, the dielectric windowis always arranged so as to extend preponderantly in the range of strongelectric fields of the ultra high frequency Waves which are to betransmitted. In the event that the operatively effective surface of thewindow extends parallel to the electric field vector, it is verydifiicult to transmit high loads, owing to the great losses occurring inthe window. Moreover, there is the danger of electrical breakdown alongthe surface of the window.

In order to prevent the danger of electrical breakdown in a dielectricvacuum-tight window which is arranged within a rectangular wave guide ina partition wall extending perpendicularly to the longitudinal axis ofthe wave guide, it is known to subdivide the window opening so as toform two slots between which extends a continuous metallic path alongthe region of the greatest electric field intensity of the TE -wavewhich is present in the wave guide. However, the losses in the windoware not particularly reduced by this measure since the two slots lie asbefore preponderantly in the region of strong electric fields of the TE-wave. Moreover, this known arrangement represents a so-called resonancewindow the band width of which is known to be relatively narrow.

There is also known a transmission system for electromagnetic ultra highfrequency waves, employing a dielectric window, such window being forthe reducing of reflections arranged so that its operatively effectivesurface extends substantially perpendicularly to the direction of theelectric field which preponderates on both sides in the transmissionchannels. An embodiment of this known transmission system comprises twocross-sectionally rectangular wave guide parts disposed in overlappingrelation with the longitudinal axes extending in parallel, and having adielectric window inserted at the juncture of the two wave guide parts.It was found that difficulties arise in connection with such anarrangement so far as the prevention of the triggering of undesired wavetypes (interference modes) is concerned. However, interference modesbring about considerable disturbance in the matching of the transmissionchannels to the window, causing in turn electrical field increases atthe window and consequently an impermissible heating thereof.

In order to overcome the indicated difficulties, the invention proposesto provide in connection with an ultra high frequency system of theinitially mentioned type, a coupling opening in the form of an arcuateslot which is arranged preponderantly outside a region of strongelectric fields of the ultra high frequency waves which are present inthe two wave guides, such slot partially embracing the respectiveregion, and the total length of the slot of the coupling opening oropenings exceeding half of the average operating wave length of thetransmission system.

The magnetic field is as is known very strongly pronounced in a waveguide at the place of slight electric field intensity. In a transmissionsystem according to the invention, there is therefore a strong magneticcoupling between the two wave guides which are arranged at the sides ofthe dielectric window. This magnetic coupling necessarily presupposesthat the electric field vector is in the region of the coupling openingoriented parallel to the plane in which is disposed the coupling openingand therewith parallel to the surface of the dielectric window. Thelosses at the window are nevertheless extraordinarily slight since theelectric field appearing in the slot is quite weak owing to the strongmagnetic field. The coupling slot is advantageously of a configurationso that it extends approximately parallel to a magnetic field line whichis present in the two wave guides at the place of great magnetic fieldintensity at average operating wave length.

The coupling slot of a transmission system according to the inventionmay be considered as a short-circuited Lecher line. Since anelectromagnetic field is formed in a short-circuited line only in thevicinity of a resonance, the length of the slot is advantageously sodimensioned that the inherent resonance thereof lies approximately inthe center of the desired transmission range of the system. The loadcoupled to the transmission system reduces the quality of the slot linevery much so that the transmission range of the system becomes great. Ithas been found that a band width of one whole octave can be obtainedwith a transmission system according to the invention. Appropriateselection of the inherent resonance of the slot line makes it possibleto provide for a condition in which all interference resonances of theslot line lie outside of the transmission range.

The various objects and features of the invention will appear from theappended claims and from the description of embodiments thereof which isrendered below with reference to the accompanying drawings.

FIGS. 1 and 2 indicate an embodiment of the invention as to theprinciples involved;

FIGS. 3 and 4 illustrate a structurally simple embodiment of thetransmission system according to the invention; FIG. 4 representing asectional view along the lines C-D in FIG. 3;

FIG. 5 shows in sectional view an embodiment in which the dielectricwindow is disposed between the overlapping wall parts of the two waveguides, a coupling slot being provided on each side of the window;

FIGS. 6 and 7 represent sectional views respectively along lines E-F andG-H of FIG.

FIG. 8 indicates an embodiment somewhat similar to the one shown in FIG.5, but having a coupling slot only on one side of the window;

FIG. 9 shows an embodiment of the invention corresponding generally tothe one represented in FIG. 8 but permitting a particularly simpleassembly of parts; and

FIGS. 10 and 11 indicate in schematic manner an embodiment in which thetwo wave guides extend in perpendicularly crossing planes, FIG. 10showing the arrangement from the top and FIG. 11 showing it from theside.

Referring now to FIGS. 1 and 2, the cross-sectionally rectangular waveguide 1 overlaps with its free end a further cross-sectionallyrectangular wave guide 2 Which extends parallel to the longitudinal axisof the wave guide 1 and is staggered with respect thereto. Anelectromagnetic ultra high frequency wave is to be fed into the waveguide 1 in the direction of the arrow 3, such wave being propagatedwithin the wave guide 1 in the form of an TE -wave. The ultra highfrequency energy is from the wave guide 1 conducted into the wave guide2 by way of coupling opening 4 which is arranged in the overlappingparts of the walls of the two wave guides and which is closedvacuum-tight by means of a dielectric material. As will be seen fromFIG. 2, the coupling opening 4 is formed by an arcuate slot (couplingslot) which extends predominantly outside the range of strong electricfields of the TE -wave which spreads within the wave guide 1. The shapeof the coupling slot is approximated to the shape of a magnetic fieldline H, shown in dash lines, at the place of great magnetic fieldintensity. It will also be seen that the length of the slot must begreater than would correspond to half the average operating wave lengthof the transmission system. (The limit wave length of the magneticfundamental wave in the rectangular wave guide corresponds, as is known,to twice the width of the wave guide.) The coupling slot 4 is thenoperative as a short-circuited Lecher line. The electric field of theLecher line is indicated by arrows E. The load flux from the wave guide1 to the wave guide 2 results from the Poynting vector S. The losses inthe dielectric which fills the coupling slot 4 are extraordinarilyslight since the dielectric is loaded only by a slight electric fieldeven in the presence of a high load fiux, owing to the strong magneticcoupling.

In the constructionally simple embodiment indicated in FIGS. 3 and 4,the rectangular wave guide 1 is soldered to the end of a delay line 5 ofa travelling wave tube, the longitudinal axis of the wave guideextending perpendicular to the longitudinal axis of the delay line. Thewave guide 1 overlaps, as in FIG. 1, a rectangular wave guide 2 whichextends parallel to the longitudinal axis of the wave guide 1 and isstaggered with respect thereto. The two wave guides 1 and 2 borderdirectly on one another with their wide sides and therefore have in theregion of the overlap a common wall.

This common wall has in the center thereof a circular breakthrough inwhich is inserted a ceramic disk 6. The ceramic disk 6 carries on eachside thereof a circular metallizing 7. In this manner is formed anannular coupling slot 4 which is filled with dielectric material, suchslot embracing a region of strong electric fields of the TE -wave whichis propagated in the two wave guides. The ceramic disk 6 with themetallizing 7 is so dimensioned that the average circumference of thecoupling slot 4 coincides in approximation with the circumference of amagnetic field line which forms at average operating wave length in thewave guides 1 and 2 at the place of greatest magnetic intensity.Moreover, the Wave impedance of the slot 4 shall for good matching ofthe wave guide junction correspond to the geometric mean of the waveimpedances of the two wave guides.

In the transmission systems according to FIGS. 1 to 4,

there is the danger that marginal currents flowing in the margin of thecoupling opening causes losses and therewith an impermissible heating ofthe metallization of the dielectric with which the dielectric issoldered in the junction between the two wave guides. In order to avoidthis danger, the dielectric is not directly inserted in the couplingopening, but the dielectric window is instead advantageously arranged inthe space between the overlapping wall parts of the two wave guides.FIG. 5 shows a corresponding arrangement in sectional view, FIGS. 6 and7 show, as noted before, respectively sections along the lines E-F and6-H in FIG. 5.

As will be seen from these figures, there is provided in the respectivemutually overlapping wall parts of the wave guides 1 and 2, an arcuatecoupling slot 4, 4, which is interrupted once in the range of thelongitudinal symmetry plane of the two wave guides 1 and 2 in a similarmanner as in FIGS. 1 and 2. The two coupling slots 4 and 4' are as shownin FIGS. 6 and 7 mutually displaced by Between the two coupling slots 4and 4' is disposed the dielectric window 8 which is in the form of aceramic disk soldered into a cylindrical metal ring 9 whichinterconnects the two wave guides. The cylindrical ring 9 shall bedimensioned so that the load fiux passes directly from the coupling slot4 to the other coupling slot 4. This can be achieved by appropriatedimensioning of the impedance of the junction member which is formed bythe cylindrical metal ring 9. A triggering of this junction member canalso be prevented when the inhert resonance thereof lies outside of thepass range of the transmission system. If no independent oscillation canform within the metal ring 9, there will not appear any electric fieldcomponents perpendicularly to the surface of the window and therewith noWall currents.

It is not necessary that there is in a transmission system a couplingslot on each side of the window as shown in FIGS. 5-7. It will besufiicient to provide merely in one of the two wave guides a couplingslot according to the invention, while the other wave guide is providedwith a circular hole formed therein which borders on the window, asshown in FIG. 8. The dielectric Window 8 borders in such arrangementrespectively directly on the coupling slot 4 and on the hole 10. Thecoupling slot 4 is advantageously arranged on the vacuum side of thewindow 8.

FIG. 9 shows an embodiment of the invention which correspondssubstantially to the transmission system indicated in FIG. 8 and enablesa particularly simple assembly of the system. The opening 10 in the waveguide 2 is in this case so dimensioned that its diameter is equal to thediameter of the copper ring 9 in which is inserted the window -8. Thewave guide 2 can be simply placed upon the ring 9 which is with thewindow 8 disposed on the wave guide 1 above the coupling slot 4.

It may be mentioned at this point that the wave guides 1 and 2 which aredisposed in the arrangement according to FIGS. 19 in parallel planes,can also be arranged so as to extend perpendicularly to one another, asincheated in FIGS. 10 and 11, wherein 'FIG. 10 shows the two wave guidesfrom the top while FIG. 11 shows a side view thereof.

The invention is not inherently limited to the described and illustratedembodiments. It is, for example, not necessary that the wave guides,which are mutually closed by the vacuum-tight window, extend in parallelone with respect to the other. The coupling slot provided according tothe invention, may also be situated in a partition wall extendingperpendicularly to the axis of the wave guides and terminating one waveguide. The coupling slot extends in such a case along the margin of thepartition wall and is interrupted in the region of the narrow side f therectangular wave guide. Experiments have revealed that a good matchingextending to the load can in such case likewise be obtained over anextraordinarily broad frequency band. It may also be mentioned that thecoupling slot provided according to the invention may be interruptedseveral times. It is thereby merely important that the individualcoupling slots are by their own scattering fields mutually coupled insuch a manner that they constitute a slot line (line length greater thanhalf the average operating wave length). It is also feasible to usecircular instead of rectangular wave guides. The basic disadvantage ofcircular wave guides which resides in that the wave field is notdefinite, can be remedied by the provision of protuberances, slots orthe like, formed therein.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

We claim:

1. A transmission system for electromagnetic ultra high frequency waves,especially for use in connection with high capacity ultra high frequencytubes, including two wave guides which are mutually connected by way ofat least one slot-like coupling opening which is closed vacuum-tight bya dielectric window and through which the electromagnetic wave energypasses from one to the other wave guide, thereby characterized that thecoupling opening extends arcuately in slot-like manner preponderantlyoutside a region of strong electric fields of the ultra high frequencyoscillations which are present in the two wave guides, and whichpartially embraces such region, the total length of the coupling openingexceeding half the average operating wave length of the transmissionsystem.

2. A transmission system according to claim 1, wherein said wave guidesare substantially identically dimensioned cross-sectionally rectangularwave guides which conduct an TE -wave.

3. A transmission system according to claim 2, wherein said wave guidesextend parallel to one another, mutually staggered and with the broadsides in overlapping relationship, said coupling slot being arranged inthe region of the overlap of said wave guides.

4. A transmission system according to claim 2, wherein said wave guidesextend in two parallel mutually perpendicularly crossing planes with onewave guide in overlapping relationship with respect to the other waveguide, said coupling slot being arranged in the region of the overlap ofsaid wave guides.

5. A transmission system according to claim 2, wherein said wave guidesextend parallel to one another, mutually staggered and with the broadsides in overlapping relationship, said coupling slot being arranged inthe region of the overlap of said wave guides and being of aconfiguration approximating the shape of a magnetic field line which ispresent in the two wave guides at the place of great magnetic fieldintensity at average operating wavelength.

6. A transmission system according to claim 5, said wave guides beingdisposed directly contiguous with one wall common to both wave guides, acircular opening being formed in said common wall in which is disposed aceramic disk carrying a metallization on each side thereof so as to forma circular marginally extending window.

7. A transmission system according to claim 5, said coupling slot beinginterrupted once in the region of the longitudinal symmetry plane of thetwo wave guides.

3. A transmission system according to claim 2, wherein said wave guidesextend in two parallel mutually perpendicularly crossing planes wit-hone wave guide in overlapping relationship with respect to the otherwave guide, said coupling slot being arranged in the region of theoverlap of said wave guides and being of a configuration approximatingthe shape of a magnetic field line which is present in the two waveguides at the place of great mganetic field intensity at averageoperating wave length.

9. A transmission system according to claim 8, said 6 wave guides beingdisposed directly contiguous with one wall common to both wave guides, acircular opening being formed in said common wall in which is disposed aceramic disk carrying a metallization on each side thereof so as to forma circular marginally extending window.

10. A transmission system according to claim 8, said coupling slot beinginterrupted once in the region of the longitudinal symmetry plane of thetwo Wave guides.

11. A transmission system according to claim 2, wherein said wave guidesextend parallel to one another, mutually staggered and with the broadsides in overlapping relationship, said coupling slot being arranged inthe region of the overlap of said wave guides and being of aconfiguration approximating the shape of a magnetic field line which ispresent in the two wave guides at the place of great magnetic fieldintensity at average operating wave length, said window being inserteddirectly in said coupling slot.

12. A transmission system according to claim 2, wherein said wave guidesextend in two parallel mutually perpendicularly crossing planes with onewave guide in overlapping relationship with respect to the other waveguide, said coupling slot being arranged in the region of the overlap ofsaid Wave guides and being of a configuration approximating the shape ofa magnetic field line which is present in the two wave guides at theplace of great magnetic field intensity at average operating wavelength, said window being inserted directly in said coupling slot.

13. A transmission system according to claim 2, wherein said wave guidesextend parallel to one another, mutually staggered and with the broadsides in overlapping relationship, said coupling slot being arranged inthe region of the overlap of said wave guides and being of aconfiguration approximating the shape of a magnetic field line which ispresent in the two wave guides at the place of great magnetic fieldintensity at average operating wave length, said window being in theform of a disk made of dielectric material inserted within a cylindricalring-shaped member and disposed in the space between the overlappingwall portions of the two wave guides and mutually interconnecting saidwave guides.

14. A transmission system according to claim 13, wherein said windowborders directly on the coupling slot.

15. A transmission system according to claim 14, wherein a coupling slotis formed in each of the overlapping walls of the two wave guides, saidslots being mutually displaced by 16. A transmission system according toclaim 14, wherein only one wave guide is provide with a coupling slotwhich is directed toward the window while the other wave guide isprovided with a circular opening formed therein which faces said window.

17. A transmission system according to claim 13, wherein a coupling slotis formed in each of the overlapping walls of the two wave guides, saidslots being mutually displaced by 180.

18. A transmission system according to claim 13, wherein only one waveguide is provided with a coupling slot which is directed toward thewindow while the other wave guide is provided with a circular openingformed therein which faces said window.

19. A transmission system according to claim 18, wherein said couplingslot is formed in the Wave guide lying on the vacuum side.

20. A transmission system according to claim 19, wherein the cylindricalring in which is inserted the window, is fitted in the opening formed inthe wave guide facing away from the vacuum space.

21. A transmission system according to claim 2, wherein said wave guidesextend in two parallel mutually perpendicularly crossing planes with onewave guide in overlapping relationship with respect to the other waveguide, said coupling slot being arranged in the region of the overlap ofsaid wave guides and being of a configuration approximating the shape ofa magnetic field line which is present in the two wave guides at theplace of great magnetic field intensity at average operating Wavelength, said window being in the form of a disk made of dielectricmaterial inserted within a cylindrical ring-shaped member and disposedin the space between the overlapping wall portions of the two waveguides and mutulally interconnecting said wave guides.

22. A transmission system according to claim 21, Wherein said windowborders directly on said coupling slot.

23. A transmission system according to claim 22, wherein a coupling slotis formed in each of the overlapping walls of the two wave guides, saidslots being mutually displaced by 180.

24. A transmission system according to claim 22, wherein only one waveguide is provided with a coupling slot which is directed toward thewindow while the other wave guide is provided with a circular openingformed therein which faces said Window.

25. A transmission system according to claim 21, wherein a coupling slotis formed in each of the overlapping walls of the two wave guides, saidslots being mutually displaced by 180".

26. A transmission system according to claim 21, wherein only one waveguide is provided with a coupling slot which is directed toward thewindow while the other wave guide is provided with a circular openingformed therein which faces said window.

References Cited by the Examiner UNITED STATES PATENTS 2,602,859 7/52Moreno 333-10 HERMAN KARL SAALBACH, Primary Examiner.

1. A TRANSMISSION SYSTEM FOR ELECTROMAGNETIC ULTRA HIGH FREQUENCY WAVES,ESPECIALLY FOR USE IN CONNECTION WITH HIGH CAPACITY ULTRA HIGH FREQUENCYTUBES, INCLUDING TWO WAVE GUIDES WHICH ARE MUTUALLY CONNECTED BY WAY OFAT LEAST ONE SLOT-LIKE COUPLING OPENING WHICH IS CLOSED VACUUM-TIGHT BYA DIELECTRIC WINDOW AND THROUGH WHICH THE ELECTROMAGNETIC WAVE ENERGYPASSES FROM ONE TO THE OTHER WAVE GUIDE, THEREBY CHARACTERIZED THAT THECOUPLING OPENING EXTENDS ARCUATELY IN SLOT-LIKE MANNER PREPONDERANTLYOUTSIDE A REGION OF STRONG ELECTRIC FIELDS OF THE ULTRA HIGH FREQUENCYOSCILLATIONS WHICH ARE PRESENT IN THE TWO WAVE GUIDES, AND WHICHPARTIALLY EMBRACES SUCH REGION, THE TOTAL LENGTH OF THE COUPLING OPENINGEXCEEDING HALF THE AVERAGE OPERATING WAVE LENGTH OF THE TRANSMISSIONSYSTEM.